DETERMINATION OF RESIDUALS STRESSES AROUND BLISTERS IN ZR-2.5%NB PRESSURE TUBES Javier. R. Santisteban 1 , Axel Steuwer 2 , Gladys Domizzi 3 , Mathew Peel 4 1 Centro Atómico Bariloche CONICET e Instituto Balseiro Bariloche (8400) - ARGENTINA 2 Fame38 at the ESRF-ILL 38042 Grenoble – FRANCE 3 Centro Atómico Consituyentes CNEA – Av. Libertador 8250 Buenos Aires (1429) - ARGENTINA 4 European Synchrotron Radiation Facility 38042 Grenoble – FRANCE ABSTRACT We have used synchrotron X-ray diffraction experiments to measure the strain field introduced by a hydride blister grown on a section of a pressure tube from a CANDU nuclear reactor. After charging the tube section with a homogeneous hydrogen concentration of 300 wt ppm, the blister was produced by creating a small cold spot on its surface (~200 o C), while the bulk was kept at a temperature of 338 o C over a period of 1008 hours. The blister studied here is ellipsoidal in shape, with its long axis along the tube axial direction. The experiments were performed on the wiggler beam line ID15 at the European Synchrotron Radiation Facility (ESRF), using a polychromatic beam of high-energy X-rays (60-300keV). Unlike conventional X-ray diffraction, in this mode the scattering angle is fixed and the diffracted beam is discriminated on the basis of the photon energy. The results show that the blister is composed by two crystallographic phases (δ-ZrH and α-Zr), with volume fractions varying with position. The maximum stresses appear at the blister- matrix interfaces. Near the tube outer surface, we found large compressive stresses of (-450±90) MPa along the blister long axis, and tensile stresses (+320±90) MPa along the tube hoop direction. The main uncertainty in these stresses results from the uncertainty in the elastic constants of the hydride phase. Large strains and broad peaks were observed for this phase, which were explained by a rather low Young modulus (35GPa) for the hydride. The results are compared with finite elements simulations found in the literature. INTRODUCTION In CANDU nuclear power reactors, pressure tubes of cold-worked Zr-2.5%Nb material are used in the reactor at operation temperatures ~300 o C. Over time, the pressure tubes absorb a small fraction of the deuterium (D) from the heavy water used as coolant. Cold spots due to the unexpected contact with other reactor components introduce thermal gradients within the tube. These gradients lead to the redistribution of D and the precipitation of hydrides, which can result in the formation of hydride blisters at the cold spot, and ultimately to the tube failure [1]. Hydride blister formation is also a relatively common mode of failure on Zircaloy-4 fuel cladding [2]. 577 Copyright ©JCPDS-International Centre for Diffraction Data 2009 ISSN 1097-0002